<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style type="text/css">
		.box {
			width: 343px;
			height: 200px;
			background: url(paopao.png) no-repeat left top,
						rgba(0,0,0,.5) url(paopao.png) no-repeat right bottom;

			transition: all 2s linear;
		}

		.box:hover {
			background-position: left bottom,
								 right top;
		}
	</style>
</head>
<body>
	
	<div class="box"></div>
</body>
</html>